Carboxymethylmercapto compounds as stabilizers for photographic emulsions



CARBOXYMETHYLMERCAPTO COMPOUNDS AS FOR PHOTOGRAPHIC EMUL- Thomas F. Murray, George A. Reynolds, and James A. Van Allan, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application February 23, 1956 Serial No. 567,418

14 Claims. (Cl. 96-409) tion; in this invention, we are not concerned with the latter.

Fog depends both on the emulsion and the conditions of development; for a given emulsion it increases with the degree of development. With constant development conditions, it tends to increase with time, temperature and relative humidity of storage conditions; it is common practice to make accelerated tests of the stability of photographic emulsions by storage at increased temperature or humidity, or both. It 1s, of course, desirable to have emulsions as stable as possible under the conditions of high temperature and humidity which may occur in tropical climates, for example. Fog usually appears over the whole area of the sensitive coating, but when severe, it frequently is non-uniform. Fog may also be caused by exposure to chemicals, for example, hydrogen sulfide and other reactive sulfur compounds, hydrogen peroxide vapor, and strongly reducing materials. While antifoggants and stabilizers may protect, to some extent, against such efiects, it is normally understood that an antifoggant protects against spontaneous growth of fog during prolonged storage or storage at high temperatures and humidities, or during development to maximum contrast and speed, or both.

It is, therefore, an object of the present invention to provide a method for stabilizing photographic emulsions. A further object is to provide a means for reducing the fog produced upon keeping of such emulsions which have been sensitized, especially emulsions stored under tropical or other adverse conditions. A still further object is to provide a means for stabilizing the speed and contrast of sensitized photographic emulsions. Other objects will become apparent from a consideration ofthe following description and examples.

It is known that certain mercaptans, and particularly compounds having mercapto substitution on a heterocyclic ring, have an antifoggant and stabilizing effect when incorporated in photographic silver halide emulsions. In general, these compounds are relatively strongly antifoggant at low concentrations but they are also desensitizing, and the concentration at which desensitization is largely avoided may be so low that the antifoggant action is weak. Conversion of the mercapto group to a thioether (alkylor arylmercapto) group usually reduces the photographic activity by a large factor. Consequently, thioethers as a class have little usefulness in photographic emulsions.

States atent O We have found that heterocyclic nitrogen compounds containing a carboxymethylmercapto substituent have strong antifoggant and stabilizing effects when incorporated in photographic silver halide emulsions. The optimum concentrations are generally higher than those of the corresponding mercaptans and are less critical with respect to desensitization. Many of our antifoggant and stabilizing compounds have a sulfur or oxygen atom in the heterocyclic ring, in addition to the nitrogen atom.

According to our invention we provide a method for stabilizing photographic silver halide emulsions by incorporating therein a simple heterocyclic nitrogen compound containing a carboxymethylmercapto substituent. By simple heterocyclic compound we mean a compound wherein the heterocyclic atoms (i. e. atoms other than carbon) are members of a single heterocyclic ring, as contrasted with compounds containing fused or condensed heterocyclic rings in which the heterocyclic atoms are members of more than one heterocyclic ring. Such simple heterocyclic nitrogen compounds include triazoles (e. g. 1,2,4-triazoles, especially those containing an amino substituent in addition to the carboxymethylmercapto substituent), diazoles (e. g.,imidazoles, benzimidazoles, imidazolines, etc.), pyrimidines (especially those wherein the carboxymethylmercapto group is in the 2-position), 1,2,4-triazines, s-triazines, mono-azoles (e. g. benzoxazo'les, benzothiazoles, etc.), etc. These carboxymethylmercapto compounds can, in general, be obtained from the corresponding mercapto compounds by the well known Williamson synthesis, wherein the alkali metal salt of the mercapto compound is condensed with an alkaline solution of chloroacetic acid (salt). This method is further illustrated below.

These simple heterocyclic compounds can advantageously be represented by the following general formula:

R 1 N C-S- H-COOM wherein R represents a hydrogen atom or an alkyl group (e. g., methyl, ethyl, butyl, heptyl, etc.), M represents a hydrogen atom or an alkali metal atom (e. g., sodium, potassium, etc.), and Z represents the non-metallic atoms necessary to complete a simple heterocyclic ring as defined above.

Compounds useful in practicing our invention include those represented by the following formulas (R means carboxymethylmercapto) 2-carboxymethylmercapto-4-methylimidazo1ine C-Rr 2-carboxymethylmercaptoimtdazollne Pa tented Jan. 14, 1958 2.-carboxymethylmereapto-l-phenylimidazole H2O NCH2CO 0H H cl 2-carboxymethylmercaptoimldazoline chloroacetate Z-CarboXymethyImercaptoA,G-diaminopyrimidlne (8.) N

HQN Wen HsNl/ I THg Z-carboxymethylmercapto-4,5,G-triaminopyrtmldine I NHg 4am:ino-2rcarboxymethylmercapto-6-hydroxypyr1midine (10.), N

k/IR.

2-carboxymethylmercaptopyrimidine 11. N H3O YR].

I OH

2-carboxymethylmercaptol-hydroxy-fimethylpyrimidine 11m, V 2-carboxymethylmercapto-4,6-diamino-s-triaztne NH, 4,6-dlamino-2-(l-carhoxyoctylmercapto)-s-triazine Z carbQxymethylmercaptobenzoxazole C-Rg 2-carboaymethylmercaptobenzothiazole C-Rt 2-carboxymethylmercaptobenzimidazole By carboxymethylmercapto we mean the group:

or such a group having a simple substituent, such as alkyl (e. g., methyl, ethyl, butyl, heptyl, etc.), attached to the CH carbon atom.

The principal purpose of our invention is to provide a means for maintaining the sensitivity and fog of silver halide emulsions at or close to initial optimum values under conditions of high temperature or high humidity, or both. Preferably, the antifoggants of our invention are added to the emulsion at any stage during the process of manufacture prior to coating the emulsion. The antifoggants can be added to the emulsion in solution in water or any convenient solvent not injurious to the emulsion, such as lower aliphatic alcohols, acetone, etc.

The solutions of antifoggants which we employ when added in suitable concentration before coating to unsensitized or optically sensitized silver halide emulsions usually do not appreciably afiect the sensitivity and fog when measurements are made soon after coating. However, when sensitometric measurements are made after appreciable intervals of time under tropical or dry conditions of storage at elevated temperatures, the antifoggants do stabilize speed and maintain fog at a low level.

The preparation of silver halide emulsions involves three separate operations: (1) the emulsification and digestion or ripening of the silver halide, (2) the freeing of the emulsion from aqueous soluble salts usually by washing, (3) the second digestion or after-ripening to obtain increased sensitivity (Mees, The Theory of the Photographic Process, 1942, page 3). The fog inhibiting agents can be added at any stage, preferably after the final digestion.

The photographic emulsions which we use are of the developing-out type and best results have been obtained with gelatino-silver bromoiodide emulsions. sions of varying halide composition can be used.

The emulsions can be chemically sensitized by any of the accepted procedures. The emulsions can be digested With naturally active gelatin, or sulfur compounds may be added such as those described in Sheppard U. S. Patent 1,574,944 and U. S. 1,623,499, and Sheppard and Brigham U. S. Patent 2,410,689.

The emulsions can also be treated with salts of the noble metals such as ruthenium, rhodium, palladium, iridium and platinum, all of which belong to group VIH of the. periodic table of elements and have an atomic weight greater than 100. Representative compounds are. ammonium chloropalladate, potassium chloroplatinate and sodium chloropalladite, which are used for sensitizing in amounts below that which produces anysubstantial fog inhibition, as described in Smith and Trivelli U. S. Patent 2,448,060, and as anti-foggants in higher amounts, as described in Trivelli and Smith U. S. Patents 2,556,245 and 2,566,263.

The emulsions can also be chemically sensitized with gold salts as described in Waller and Dodd U. S. Patent 2,399,083, or stabilized with gold salts as described in Damschroder U. S. Patent 2,597,856 and Yutzy and Leermakers U. S. Patent 2,597,915. Suitable compounds are potassium chloroaurite, potassium aurithiocyanate, potassium chloroaurate, auric trichloride and Z-aurosulfobenzothiazole methochloride.

The. emulsions can also be chemically sensitized with reducing agents, such as stannous salts (Carroll U. S. Patent 2,487,850), polyamines such as diethylene triamine (Lowe and Jones U. S. Patent 2,518,698), poly-- However, emul amines such as spermine (Lowe and Allan U. S. Patent 2,521,925), or bis-(,B-aminoethyDsulfide and its watersoluble salts (Lowe and Jones U. S. Patent 2,521,926).

The emulsions can also be stabilized with the mercury compounds of Allen, Byers and Murray U. S. application Serial No. 319,611 (nowU. S. Patent 2,728,663, issued December 27, 1955); Carroll and Murray U. S. application Serial No. 319,612 (now U. S. Patent 2,728,664, issued December 27, 1955); and Leubner and Murray U. S. application SerialNo. 319,613 (now U. S. Patent 2,728,665, issued December 27, 1955), all filed November 8, 1952.

The antifoggants of our invention are effective in the presence or absence of optical sensitizing dyes. Since optical sensitizing can atfect stability of emulsions with respect to sensitivity, fog and latent image changes, the action of the antifoggants is not completely independent of optical sensitizing or other emulsion variables. We have found, however, that both unsensitized emulsions and emulsions sensitized with cyanine or merocyanine dyes, or both, can be treated with the antifoggant comspeed,,gamma and fog, before and after incubation of each of the samples, are given in the following table. Kodak Developer D-19 has the following composition:

Water, about 125 F cc 500 Water to make one liter.

Kodak Developer SD-28 has the following composition:

pounds represented by Formula I above. Grams The quanuty of antifoggant compound employed can N- nethyl-p-ammophenol sulfate 1.5 be vaned, dependmg upon the particular silver hahde Hydroqumone 1.3 employed, degree of ripening, presence or absence of Sodium sulfite (des1ccated) 75 other emulsion addenda, etc. In general, the quanuty of Borax 4.5 anhfoggant can vary from about 0.01 to 3.0 grams per Potassmm brom1de 0.4 gram mole of s1lver halide 1n the emulsion. These Water to make one llter.

Ineu- Development Fresh Tests Incubation Tests Compound batlon Example (gJmol. Time .AgX) (wks.) Time Developer /E Gamma Fog 30/E Gamma Fog (Mms.) Speed Speed Control.-. 1 5 DK-50 5, 350 1. 12 .19 2, 100 .96 .45 1. (1.5)--.- 1 5 DK-50 4, 350 1.15 .15 2,950 1.03 .20 Control 1 5 DK-50 5, 350 1. 22 15 4, 050 1. 05 .24 2. .3) 1 5 DK-50 5,350 1.23 .13 4,350 1.12 .15 Control--. 1 5 DK-5O 6, 900 1. 00 10 6, 400 1. 03 19 1 5 DK-50 6, 400 1. 06 11 3, 150 1.17 12 1 5 DK-50 6, 900 1.00 10 6, 400 1. 03 .19 1 5 DK-5O 5, 100 1. 02 09 4,450 1. 01 10 2 12 SD-28 3, 450 .92 .09 2, 200 .74 .24 2 12 sD-2s 3, 450 .96 10 2, 600 77 .20 1 5 DK-5O 6, 700 1. 00 15 5, 700 .90 20 1 5 DK-SO 6, 900 1. 05 14 3, 950 1. 00 15 1 5 DK-50 5, 209 1. 13 17 2, 600 1. 02 33 1 5 DK-50 4, 350 1. 14 16 3, 100 1. 04 22 1 6. 5 s1) 2s 2, 200 .83 11 1, 090 65 .19 1 6. 5 SD-28 2, 200 .73 12 1, 440 .67 16 1 5 DK-50 7, 050 1. 0s 10 6, 700 94 16 1 5 DK-50 7,700 1. 04 .07 6, 150 .99 .12 1 4 D-19 2, 800 1. 19 3, 800 1.59 .23 1 4- D-19 3, 350 1.50 .17 3, 600 1. 30 .20 1 5 DK- 7, 050 1. 0s 10 6, 700 .94 16 1 5 Inc-50 2,1100 1. 14 .07 3,000 1.10 .08 1 5 DK-5O 6,700 1. 00 15 5, 700 90 20 1 5 DK-50 6, 400 1. 02 14 6, 250 .90 17 2 5 DK-50 4, 850 1. 14 13 4, 750 1.18 .26 2 5 DK-50 3, 100 93 15 2, 350 1. 02 22 2 5 DK-50 4, 350 1. 25 16 2, 150 95 .36 15. (.75)--. 2 5 DK-50 4, 750 1.26 .14 2,450 .99 .20. Control--. 2 4 D-19 4,350 1.32 .12 1,730 .83 .62 16. (.15)--. 2 4 D-19 3,950 1.23 .11 2,000 .93 .52

amounts can be used in combmanon with one or more in a manner similar to that illustrated in the above of the chem1cal sens1t1z1ng and stabilizing agents listed examples, other compounds of our 1nvent1on can be used above.

The stabilizing action afiorded by the antifoggants of our invention was determined by incubation of the emulsions for a period of 1 to 2 weeks at 120 F. (as indicated below) and at constant humidity. The speeds were measured in terms of 30/E Where E is the exposure in meter candle seconds required to produce a density of 0.2 above fog. The antifoggants were added to a panchromatically-sensitized, high speed silver bromiodide emulsion which had been chemically sensitized with a sulfur compound, such as described in Sheppard U. S. Patent 1,574,944 and potassium chloroaurate. The emulsions were then coated on a cellulose acetate support and the coatings exposed on an Eastman lb Sensitometer and processed for the time indicated below in a developer of the type indicated below. The results of these tests for to stabilize photographic silver halide emulsions, either in the presence or absence of chemical sensitizers.

Instead of incorporating the antifoggants in the photographic silver halide emulsion, these antifoggants can be incorporated in a colloid layer, such as a gelatin overcoating layer or interlayer, in contact with the emulsion.

The fog-inhibiting agents which we have described can be used in various kinds of photographic emulsions. In addition to being useful in non-sensitized emulsions, they can also be used in orthochromatic, panchromatic, and X-ray emulsions. if used with sensitizing dyes they can be added to the emulsion before or after the dyes are added. Various silver halides can be used as the lightsensitive material, including silver bromide, silver iodide, silver chloride, silver bromiodide, silver chlorobromide, silver chlorobromiodide, etc. The antifoggants of our .7 invention cantbe used in emulsions intended for color photography, for example, emulsions containing colorforming couplers, or emulsions to be developed by solutions containing couplers.

The dispersing agents can be gelatin, or other colloids, such as collodion, albumen, cellulose derivatives, synthetic resins, etc.

These carboxymethylrnercapto compounds can, as mentioned above, be obtained from the corresponding mercapto compounds by condensing an alkali metal salt of the mercapto compound with an alkaline solution containing an alkali metal chloroacetate. This method of making the carboxymethylmereapto compounds of our invention is illustrated in U. S. Patent 2,527,265, issued October 24, 1950. Other examples follow.

Example A.-2 carboxymethylmercapto-I -phenylz'midazole KIJaHs HC-N A mixture of 3.5 grams of 1-phenyl-2(3H)-imidazolethione, 3.0 grams of sodium chloroacetate and 15 ml. of water was heated on the water bath for 15 minutes, then 2.0 grams of sodium carbonate was added, and the mixture refluxed 0.5 hour. The clear solution was filtered, and acetic acid was added. The product separated as a white precipitate which was filtered, washed and dried. Yield, 3.5 grams, M. P. l48-50 C.

Example B.2-carboxymethylmercapto 4,6 diaminopyrimidine N-C-NH: HOOCCHzS-(il ("3H N=CNH:

A mixture of 15 grams each of 4,6-diamino-2-mercaptopyrimidine and sodium chloroacetate, 10 grams of sodium bicarbonate in 100 ml. of water was heated on the steam bath. After 0.5 hour, complete solution ensued. Heating was continued for one hour. The reaction mixture was treated with decolorizing carbon, filtered, and acidified with acetic acid. The precipitate was filtered and dried to give 17 grams of product, M. P. 2703 C.

Analysis for C H O N S: Calcd: C, 36.0; H, 4.0. Found: C, 35.5; H, 4.1.

In a manner similar to that illustrated in Example B above, Z-carboxymethylmercapto 4,5,6 triaminopyrimidine (compound 8) was prepared by replacing the pyrimidine compound used in Example B by a molecularly equivalent amount of 2-mercapto-4,S,6-triaminopyrimidine.

Example C.2-carboxymethylmercapro 4 amino-fi-hydroxypyrimidine N=?NH: HOOGCHzS-(J CH N-c-OH A mixture of 14 grams each of 4-amino-6-hydroxy-2- mercaptopyrimidine and sodium chloroacetate in 150 ml. of water was refluxed for 1.5 hours, then 3 grams more of sodium chloroacetate in 50 ml. of water was added. After a further hour on the steam bath, the precipitate which formed was filtered from the hot solution and dried to give 14 grams of product. The crude product was recrystallized from 800 ml. of water to give 10 grams of pure product, M. P. 241-2" C.

Example D.2-carboxymethylmercaptopyrimidine li H A mixture of 4.0 grams of Z-mercaptopyrimidine and 4.5 grams of sodiumchloroacetate in 50 ml. of water was heated on the steam bath 15 minutes, 3.5 grams of sodium bicarbonate added, and the heating continued one hour. After cooling, the solution was acidified with hydrochloric acid, and the solid collected and recrystallized from water to give 1.5 grams of the product, M. P. 198-200 C.

Analysis calcd for C H NO S: C, 42.4; H, 3.5; N, 16.5. Found: C, 43.2; H, 2.8; N, 16.8.

Example E.-2 carboxymethylmercapto 4 hydroxy-fi methylpyrimidine H:CC-N

Hi l -SCH2CO0H H0C=N A mixture of 28 grams each of 4-hydroxy-2-rnercapto- G-methylpyrimidine and sodium chloroacetate and 30 grams of sodium bicarbonate in 300 ml. of water were refluxed for 1.5 hours. Complete solution ensued. The reaction mixture was filtered through a filter aid (e. g., Filter Cal), and the filtrate was acidified with concentrated hydrochloric acid. The precipitate was filtered and dried. Yield, 33 grams, M. P. 213-15 C. A sample was recrystallized from water. Heavy needle-like crystals, M. P. 213-14 C. were obtained.

Analysis for CqHgOgNzS: Calcd: C, 42.0; H, 4.0. Found C, 42.0; H, 4.4.

Example F .--2-carboxymethylmercaptobenzoxazale C-SCHgCO OH A mixture of 15.1 grams of Z-mercaptobenzoxazole and 13.0 grams of sodium chloroacetate in ml. of water was heated to reflux, and dilute sodium bicarbonate was slowly added until solution was complete, then refluxed for 10 minutes. The clear, yellow solution was filtered hot, and the filtrate was acidified with acetic acid. A nicely crystalline, yellow precipitate slowly separated from the aqueous phase. After standing overnight, the precipitate was collected by filtration and dried to give 12 grams of product, M. P. 1645 C.

Analysis for C9H7O3NS1 Calcd: C, 51.5; H, 3.3. Found: C, 51.3; H, 3.8.

In a manner similar to that illustrated in Example F above, 2-carboxymethylmercaptobenzothiazole (compound 16) was prepared by replacing the Z-mercaptobenzoxazole employed in Example F by a molecularly equivalent amount of 2-mercaptobenzothiazole. The desired product was obtained as crystals melting at 162-3 C.

Analysis for CgHqOgNSzZ Calcd: C, 48.0; H, 3.1. Found: C, 47.7; H, 3.2.

Example G.-4-amino-5-carboxymethylmercapta-S-phenyl-1,2,4-rriazole IFTH:

20 g. of 4-amino-5-mercapto-3-phenyl-1,2,4-triazole (1. C. 8.," 1952, page 4814), 15 g. of sodium chloroacetate, and 15 g. of sodium carbonate in 200 cc. of water were refluxed 18 hours. While still warm, the reaction mixture was acidified with hydrochloric acid and then cooled. It was filtered and then washed with water. Yield 16.6 g. The product melted at 184-6" C...(sintered at 144 C.).

Analysis calcd: C, 48.0; H, 4.0; N, 22.4; S, 12.8. Found: C, 47.5; H, 3.9; N, 22.4; S, 12.8.

Example H.-carboxymethylmercapto-3,4-diamin0-1,2, 4-triaz0le l o-somooon A mixture of 5 g. of 5-hydroxy-3-mercapto-6-methyl- 1,2,4-triazabenzene (Compt rend, vol. 186, page 1216), 4.1 g. of sodium chloroacetate, 30 cc. of water and 30 cc. of ethanol was boiled under reflux for 15 minutes and allowed to cool. The liquid and precipitated solid were heated on a steam bath, allowed to cool and acidified with hydrochloric acid. It was then chilled, and the solid filtered ofi. The filtrate was recrystallized from aqueous dimethylformamide, digested in ethanol and cooled. 1.0 g. of solid melting at 176-8 C. was obtained.

Another useful carboxymethylmercapto compound, 3- carboxymethylmercapto 6 methyl-S-phenyl-l,2,4-triazabenzene was prepared in substantially the same manner. It was obtained as a pale orange solid.

Example ].-2-carboxymezhylmercapt0-4,6-diaminas-triazine acetic acid were then added to the colorless solution with stirring until solution was obtained. The clear solution was then stirred for an additional 21 hours, no change in appearance taking place during this time. A small amount of activated carbon and a filtering agent were added to the clear solution, which was then filtered. The clear filtrate was acidified with dilute acetic acid to give a white precipitate. This precipitate was collected on a filter and dried. Yield, 5.7 g. (94.5%). A small amount of the solid was recrystallized in sodium hydroxide solution, filtered, and reprecipitated in acetic acid. The dried product had a decomposition point of about 250 C.

Example K.4,6-diamin0-2-( 1 -car.boxyoctylmercapt0)- s-triazine new C-SCHCOOH N 01111: l NH,

4.74 g. of m-bromopelargonic acid, 2.86 g. of 4,6-di amino-2-mercaptopyrimidine, and 1.76 g. of sodium hydroxide were dissolved in 50 cc. of distilled water. The clear solution was stirred for 20 hours, treated with activated carbon and a filtering agent, and then filtered. The filtrate was acidified with acetic acid, whereupon a white precipitate separated. It was collected on a filter and dried in air.

- The product was redissolved in aqueous sodium hydroxide, filtered and reprecipitated in acetic acid. The precipitate was collected on a filter and dried. Yield, 5 g. (83.5%). The dried product was washed several times with petroleum ether and then dried.

In a manner similar to that illustrated in Example K above, compound 4 was obtained by heating together 102 g. of Z-mercaptoimidazoline and g. of sodium chloroacetate in 200 cc. of water. 102 g. of the desired product were obtained. In like manner, compound 3 was obtained from the corresponding mercapto compound. See Johnson and Edens-JACS, vol. 64 (1942), page 2708).

Example L.2-carboxymethylmercaptoimidazoline ch loroacetate N Bio C-SCHZCOOH HzC/NCH2C O OH 4 g. of Z-mercaptoimidazoline and 6 g. of chloroacetic acid in 15 cc. of water were heated to boiling for 5 minutes and then cooled in an ice chest. The desired product separated as white crystals. Yield 3.1 g. On recrystallization from water, it melted at 134 C.

Calcd for C H O N SCl: C, 33.1; H, 4.3. C, 33.4; H, 4.5.

We have also found that certain derivatives of the carboxymethylmercapto compounds of our invention can also be employed to advantage as stabilizers in photographic silver halide emulsions. For example, compounds containing a carbalkoxylmethylmercapto group or a carbamylmethylmercapto group can sometimes be employed to advantage in photographic emulsions. The following two examples will describe the preparation of two compounds of these types which can be employed to advantage in photographic emulsions.

Found Example M.2-carbamylmethylmercaptoimidazoline hydrochloride 2C-IIIH H2O CS CH2 (L-NHLHCI yield of 2-carbamylmethylmercaptoimidazoline, M. P.

139-40 C., was 16 g.

Analysis for C H ON S.HCl: Calcd: C, 30.7; H, 5.1. Found: C, 30.9; H, 5.4.

Example N.2-carbethoxymethylmercaptoimidazolium hydrochloride 2O C-SOHiCOOCzHr A mixture of 10.2 g. of ethylenethiourea and 13.0 g. (11.3 ml.) of ethyl chloroacetate in 30 ml. of absolute alcohol was refluxed for 3 hours after which 60 ml. of acetone was added to the reaction mixture. The product which had separated was filtered off and recrystallized from isopropanol to give 21 g. of Z-carbethoxymethylmercaptoimidazolium hydrochloride, M. P. 1423 C.

11 1 Analysis for C H O N SCI: Caled: C, 37.4; H, 5.8. Found: C, 37.6; H, 5.7.

In general, compounds such as those represented by Examples M and N above, are not nearly so useful in photographic emulsions as are the carboxymethylmercapto compounds illustrated above.

The antifoggant and stabilizing compounds of our invention which contain a benzene ring can have substituents on the benzene ring, such as chlorine, bromine, methyl, ethyl, phenyl, etc. These compounds can be prepared in exactly the manner shown in the above examples.

What we claim as our invention and desire secured by Letters Patent of the United States is:

1. A photographic silver halide emulsion containing a monoheterocyclic nitrogen compound containing a substituent selected from the group consisting of a carboxy methylmercapto group and a salt of a carboxymethylmercapto group, said substituent being attached to said monoheterocyclic nitrogen compound in the a-position with respect to the nitrogen atom of said nitrogen compound.

2. A photographic silver halide emulsion containing a monoheterocyclic nitrogen compound selected from those represented by the following general formula:

bl b-s-bn-ooorr wherein R represents a member selected from the group consisting of a hydrogen atom and an alkyl group, M represents a member selected from the group consisting of a hydrogen atom and an alkali metal atom and Z represents the non-metallic atoms necessary to complete a heterocyclic ring.

3. A photographic gelatino-silver-halide-developing-out emulsion containing a monoheterocyclic nitrogen compound selected from those represented by the following general formula:

I l N wherein R represents a member selected from the group consisting of a hydrogen atom and an alkyl group, M represents a member selected from the group consisting of a hydrogen atom and an alkali metal atom and Z represents the non-metallic atoms necessary to complete a heterocyclic ring.

5. A photographic silver halide developing-out emulsion containing a compound selected from those represented by the following general formula:

V N o-s-omooon wherein M represents a member selected from the group consisting of a hydrogen atom and an alkali metal atom and Z represents the non-metallic atoms necessary to complete an imidazoline heterocyclic ring.

8. A photographic gelatino-silver-halide developingout emulsion containing Z-carboxymethylmercaptoimidazoline.

9. A photographic silver-halide developing-out emulsion containing a compound selected from those represented by the following general formula:

16 b-s-crnoooivr wherein M represents a member selected from the group consisting of a hydrogen atom and an alkali metal atom and Z represents the non-metallic atoms necessary to complete a pyrimidine heterocyclic ring.

10. A photographic gelatino-silver-halide developingout emulsion containing 2-carboxymethylmercapto-4,6- diaminopyrimidine.

11. A photographic silver-halide developing-out emulsion containing a compound selected from those represented by the following general formula:

I It -s omoooM wherein M represents a member selected from the group consisting of a hydrogen atom and an alkali metal atom and Z represents the non-metallic atoms necessary to complete a 1,2,4-triazine heterocyclic ring.

12. A photographic gelatino-silver halide developingout emulsion containing 3-carboxymcthylmercapto-5- hydroxy-fi-methyl-l,2,4-triazine.

13. A photographic silver-halide developing-out emulsion containing a compound selected from those represented by the following general formula:

rt b-S-CHICOOM wherein M represents a member selected from the group consisting of a hydrogen atom and an alkali metal atom and Z represents the non-metallic atoms necessary to complete a benzoxazole heterocyclic ring.

14. A photographic gelatino-silver-halide developingout emulsion containing 2-carboxymethylmercaptobenzoxazole.

References Cited in the file of this patent FOREIGN PATENTS 699,888 Great Britain Nov. 18, 1953 

1. A PHOTOGRAPHIC SILVER HALIDE EMULSION CONTAINING A MONOHETEROCYCLIC NITROGEN COMPOUND CONTAINING A SUBSTITUENT SELECTED FROM THE GROUP CONSISTING OF A CARBOXYMETHYLMERCAPTO GROUP AND A SALT OF CARBOXYMETHYLMERCAPTO GROUP, SAID SUBSTITUENT BEING ATTACHED TO SAID MONOHETEROCYCLIC NITROGEN COMPOUND IN THE A-POSITION WITH RESPECT TO THE NITROGEN ATOM OF SAID NITROGEN COMPOUND. 